The present invention relates to construction technology, and, more particularly, it relates to a method of controlling the reversing of a device for driving holes in the earth and to devices for performing same.
The invention can be used to utmost effectiveness for driving or making holes in compacted soil.
The present invention can be also used to advantage in driving pipes and tubes into the soil, e.g. at trenchless laying of underground lines.
At present, various holes are driven in the earth with a wide use of devices actuated by a pressurized fluid, e.g. compressed air. More often than not the devices used are reversible, i.e. they can be operated in the forward mode wherein they advance through the soil and make a hole therein, as well as in the reverse mode, so that they can be retracted from the soil the back to surface.
There are also known methods of controlling the reversing of such percussive devices for driving or sinking holes in the earth, based on the air supply line being rotated. By rotating this line in either direction, a member controlling the air distribution in the device for driving holes in earth is, respectively, turned either in or out in a thread between two extreme positions. This operation results in the direction of the impacts in the percussive-action device being reversed, which is tantamount to reversing the direction of the progress of the device for driving holes in the earth.
This method is embodied in a percussive device for driving holes in earth (see, for example, the USSR Inventor's Certificate No. 238,424) comprising a cylindrical housing with a pointed forward end. The housing accomodates therein a reciprocable impact member having a hollow space in the rear portion thereof. The space receives therein a stepped-diameter tubular part secured in the housing by a threaded connection. The tubular part is movable between two positions whereat, respectively, the device is advanced in the forward and reverse directions.
Connected to the rear or tail portion of the tubular part is a compressed-air supply hose. The impact member is arranged in the housing so that its external surface defines with the internal surface of the housing the front working chamber, while the internal surface of the hollow space in the tail portion of the impact member defines with the tubular part the rear working chamber. The impact member has made therein a port adapted to establish communication between the two chambers, to effect reciprocation of the impact member, the chambers being communicated when the impact member is in the front part of the housing.
This hitherto known percussive device for driving holes in earth operates with compressed air being supplied via the hose and the tubular part into the rear chamber, whereby the impact member is driven forward and delivers an impact upon the front part of the housing at the end of its forward stroke. At this moment compressed air is supplied through the port in the impact member into the front working chamber.
The effective end face area of the impact member, acted upon by compressed air in the front chamber, being greater than the effective end face area of the same impact member, acted upon by compressed air in the rear chamber, the force urging the impact member in the rearward direction is greater than the force urging the impact member in the forward direction. Consequently, the impact member is driven rearwardly. Upon the port of the impact member clearing the rearmost end edge of the tubular part, compressed air is exhausted from the front chamber into ambient air.
Now the pressure of compressed air in the front chamber becomes short of the pressure in the rear chamber, the last-mentioned pressure equalling the supply line pressure, whereby the impact member is arrested and then driven forward once again, through its forward stroke.
Then the abovedescribed cycle of the operation of the device of the prior art in the forward mode repeats itself.
To make the device for driving holes in earth operate in the reverse mode, the tubular part is to be set to the position corresponding to the reverse operation. This is done by rotating the tubular part with aid of the supply hose connected thereto, until this tubular part is set at its rearmost position.
Now compressed air is again supplied into the rear chamber and also periodically supplied through the port in the impact member into the front working chamber, driving the impact member through successive reciprocations. However, in this case the impact member delivers impacts upon the rear or tail part of the housing, in which way the device is retracted through the hole made in the course of the operation of the device in the forward mode.
A disadvantage of this technique of controlling the device for driving holes in earth arises from the fact that after the hole has been made to a considerable length, it is difficult and in certain cases altogether impossible to transmit the controlling torque to the tubular part with aid of the supply hose. Moreover, this manner of switching the device from one mode of operation to the other one has proved to be time-consuming.
There is also known a method of controlling the reversing of a percussive action device for driving holes in the earth, based on pulling a cable and then rotating the supply hose to displace an air-distributing member, in which way the advance of the device is reversed.
This method of controlling a percussive device for driving holes in the ground is performed by a device (see the West German Pat. No. 2,340,751) comprising a cylindrical housing accomodating therein a reciprocable impact member. The impact member has a hollow space in its tail portion, receiving a tubular part secured in the housing. The external walls of the impact member define with the internal wall of the housing the front working chamber, while the walls of the hollow space in the impact member define with the end face of the tubular part the rear working chamber. The two chambers communicate via a port made in the impact member.
The tubular part has two annular lugs with two longitudinal lugs therebetween, limiting the displacement of this part in the axial direction, and also two recesses preventing rotation of this part relative to the housing. The tubular part is mounted in the axial bore of a guide element secured in the housing and having two longitudinal grooves and an aperture receiving a spring-urged retaining element connected with the remote-control cable. The abutment of the retaining element in the tubular part-retaining position projects into the recess in the body of the tubular part. Longitudinal grooves are made in the wall of the axial bore of the guide element. The annular and longitudinal lugs retain the tubular part in either one of two positions corresponding to the forward and reverse mode of the operation of the device for driving holes in ground.
In the forward mode of the operation of the last-described device of the prior art the tubular member is positioned so that the pattern of air distribution in the device provides for practically simultaneous impact of the impact member upon the foremost portion of the housing and admission of compressed air into the front working chamber. In this mode of operation the impact member is reciprocated, delivering successive impacts upon the foremost portion of the housing. Should it be necessary to reverse the device for driving holes in the ground, the tubular part is to be set to the other extreme position. This is attained by manually pulling the retaining element remote control cable, to withdraw the retaining abutment from the recess in the tubular part. Then the supply hose is rotated to rotate the tubular part with respect of the guide element, until its longitudinal lugs align with the grooves of the guide element. Under the action of the air pressure in the rear chamber, the tubular part is now displaced rearwardly of the device, into its other position. To retain the tubular part in this new position, the hose is rotated to rotate the tubular part about the latter's axis, and the cable is released for the retaining element to engage the tubular part.
In this new position it is ensured that the admission of compressed air into the front working chamber takes place earlier than in the forward mode, while the exhaust takes place relatively later, whereby the impact member now delivers impacts upon the rear portion of the device, which means that the device for driving holes in the ground is now advanced in the reverse direction.
A disadvantage of this reversing control method is the very incorporation of the cable which is apt to get tangled with the supply hose, or else to get caught by some foreign object. Moreover, the rotation of the hose is still required to reverse the device, which is difficult when the hole is relatively long.
There is further known a method of controlling the reversing of a percussive device for driving holes in ground, wherein the reversing control function is effected by cutting off and re-establishing the supply of compressed air through the feed line. In this way action is exerted onto an element controlling the direction of the progress of the device.
This reversing control method is performed by a percussive device for driving holes in earth (see the West German Auslegeschrift No. 2,105,229) comprising a cylindrical housing accomodating therein a reciprocable impact member. The impact member has a hollow space in the rear or tail portion thereof, receiving therein a tubular part secured in the housing. The external walls of the impact member define with the internal walls of the housing the front working chamber, while the walls of the hollow space of the impact member and the front end face of the tubular member define the rear working chamber. The impact member has a port made therein through which the two chambers communicate with each other to effect reciprocation of the impact member. A specific feature of the construction of the device is the incorporation of a bushing rotatable relative to the tubular member. The rotation of the bushing relative to the tubular part is provided for by the tubular part having made therein a cam groove, and the bush having a lug received in this groove.
The tubular part has in the greater-diameter portion thereof two rows of ports, while the bushing has on the greater diameter portion thereof two rows of slots, so arranged that when the bushing is rotated relative to the tubular part, it has its wall closing one row of the ports in the tubular member and opening up the other row. When the device for driving holes in the ground is to be operated in the forward mode, those ports of the tubular member are closed, which are the nearest to the front portion of the housing, and those ports are open which pertain to the tail portion of the housing. In this situation compressed air is supplied into the front working chamber upon the ports of the impact member having cleared the foremost edge of the tubular part, and the exhaust is effected through the open ports of the tubular part.
When compressed air is supplied via the hose and the tubular part into the rear working chamber, the impact member is driven toward the front portion of the housing, and in its foremost position it delivers an impact upon the housing. At this moment compressed air is admitted from the rear working chamber into the front working chamber via the ports in the impact member. Owing to the pressure differential acting upon the impact member, with the effort applied thereto from the front chamber being greater than from the rear one, the impact member commences its rearward motion. Upon the ports of the impact member aligning with the ports of the tubular part, compressed air is exhausted from the front working chamber into the ambient air.
To switch over the last-described device for driving holes in earth from forward to reverse operation, the supply of compressed air thereto is to be cut off. A spring then displaces the bushing relative to the tubular part, and, owing to the action of the cam slot, the bushing is rotated relative to the tubular part. When the compressed air supply is re-established, the bushing rotates some more relative to the tubular part. Now the ports of the tubular part, which are closer to the front portion of the housing, become open, and the rearmost ports therein are closed.
Now, when compressed air is supplied into the rear working chamber, the admission of compressed air into the front working chamber takes place earlier than at the forward mode of operation, whereas, in its turn, the exhaust is delayed, whereby the reciprocating impact member delivers impacts upon the rear or tail portion of the device.
A shortcoming of the last-described techinque of reversing the operation of a device for driving holes in the ground is that operating the device becomes hampered when either the air supply thereto is incidentally cut off, or else when the operation is to be interrupted for some reason, which involves cutting off the compressed air supply, because in both cases the mode of operation of the device is reversed, which is quite uncalled for. This becomes particularly awkward when the device is launched into earth, and the supply of compressed air is to be repeatedly turned off and on to correct the hole-making direction.